Periodically human health and lives are threatened by a breach of containment and accidental release of a reactive gas from an industrial source. Gas absorbing apparatuses known as emergency gas scrubbers are used in diverse industries such as chemicals, paper making, and water treatment to contain a sudden release of lethal and corrosive quantities of a reactive gas such as chlorine, hydrogen chloride, ammonia, phosgene, sulfur dioxide (SO2), sulfur trioxide (SO3), and nitric oxide (NO3).
Unfortunately, large quantities of a reactive gas can be released in an industrial accident. For example, cylinders containing 2,300 pounds of liquefied chlorine are used in some industrial processes. Similarly, hundreds of pounds each of hydrogen chloride, ammonia, phosgene, sulfur dioxide (SO2), sulfur trioxide (SO3), or nitric oxide (NO3) are stored and used in industry. The accidentally released reactive gas typically mixes with ambient air to form a rich reactive gas mixture (i.e., rich gas).
In order to absorb a large quantity of a reactive gas that can be discharged in an industrial accident, skilled artisans try various emergency gas scrubber designs and find them to be ineffective and inefficient. For example, scrubber designs suitable for removing relatively small concentrations of slow reacting gases (e.g., for odor control) are not effective at absorbing large amounts of a reactive gas released at a relatively high concentration. To boost scrubbing effectiveness, some emergency gas scrubbers are combined with recycling systems. One frightening combination involves recycling a reactive gas through a scrubber and back to its storage area, where people and equipment are in close proximity and vulnerable to the gas's lethal and corrosive effects.
Other emergency gas scrubber designs place an ejector venturi over a scrubbing tank containing a scrubbing liquid. The venturi is connected via a pipe to a source of scrubbing liquid and to a gas storage room containing a stored reactive gas. Upon accidental release of the reactive gas into the storage room, a scrubbing liquid is downwardly injected under high pressure through the venturi into the scrubbing tank, thereby creating a vacuum in the pipe to the gas storage room. The gas in the gas storage room is drawn through the pipe and into the venturi, where it mixes with the scrubbing liquid. The gas and scrubbing liquid pass downwardly through the venturi in a co-current flow and into the scrubbing tank, where an unabsorbed gas and liquid separate. Then the scrubbing tank releases the unabsorbed gas through an outlet. Ejector venturi designs, however, are not without flaws.
For example, U.S. Pat. No. 5,518,696 alleges that in an emergency, ejector venturi gas scrubbers absorb only about 70% by weight to 80% by weight of an accidentally released amount of a reactive gas. To absorb unabsorbed reactive gas that the venturi ejector allegedly misses, a packed tower is added downstream from the ejector venturi. To absorb a sufficient amount of the reactive gas, however, the packed tower must be undesirably large in size such that an amount of packing material in the oversized tower is substantially larger than an amount theoretically needed to absorb all of the reactive gas. For example, removing chlorine having an initial concentration (i.e., concentration prior to entering an 80% efficient venturi ejector) of 800,000 parts per million would require a tower height exceeding 3.35 meters.
Thus, U.S. Pat. No. 5,518,696 mentions an alternative once-through, multi-unit emergency gas scrubber design that uses a series of three serially connected chambers having a plurality of spray nozzles that, unlike a venturi's flow pattern, spray a scrubbing liquid countercurrent to a flow of reactive gas through the chambers. The reactive gas then passes from the last chamber to a bed that has been wetted with a scrubbing liquid. As in the chambers, the gas and the scrubbing liquid flow in opposite directions or countercurrently in the wetted bed. Unabsorbed gas then exits through a vent stack to the earth's atmosphere. The design requires three countercurrent chambers and a wetted countercurrent bed.
Not surprisingly, therefore, conventional once-through emergency gas, scrubbers typically contain multiple packing sections and are built oversized compared to what is theoretically required to neutralize an anticipated amount of a reactive gas. The scrubbers are made of expensive corrosion-resistant metal such as titanium, metal alloys such as HASTELLOY® (Haynes International, Inc.) alloys, or non-metals such as fiberglass reinforced plastics. Oversized units use large amounts of the expensive corrosion-resistant metals, metal alloys, or non-metals and their use is problematic in situations where construction budgets, space, or both is limited. Heretofore in some conventional applications, scrubber towers of more than 8 meters total height are designed.
Efficient and effective functioning of a reactive gas absorbing apparatus (e.g., scrubber) is directly related to the apparatus' design and efficient, smaller, and less expensive reactive gas apparatuses are needed. Ideally, the apparatus would be designed to minimize sizes of absorbing units and reduce numbers of the units employed. In an emergency, the apparatus would rapidly absorb a majority of an amount of a reactive gas without being hydraulically flooded by the reactive gas. Such an apparatus would be useful for scrubbing corrosive and lethal amounts of reactive gases in a health and safety setting and for preparing solutions (e.g., reagent solutions) by contacting a reactive gas to, and allowing the reactive gas to react with, a solvent in a manufacturing setting.